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Andrew Scull5e1ddfa2018-08-14 10:06:54 +01001//===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
2//
Andrew Walbran16937d02019-10-22 13:54:20 +01003// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
Andrew Scull5e1ddfa2018-08-14 10:06:54 +01006//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the MachineLoopInfo class that is used to identify natural
10// loops and determine the loop depth of various nodes of the CFG. Note that
11// natural loops may actually be several loops that share the same header node.
12//
13// This analysis calculates the nesting structure of loops in a function. For
14// each natural loop identified, this analysis identifies natural loops
15// contained entirely within the loop and the basic blocks the make up the loop.
16//
17// It can calculate on the fly various bits of information, for example:
18//
19// * whether there is a preheader for the loop
20// * the number of back edges to the header
21// * whether or not a particular block branches out of the loop
22// * the successor blocks of the loop
23// * the loop depth
24// * the trip count
25// * etc...
26//
27//===----------------------------------------------------------------------===//
28
29#ifndef LLVM_CODEGEN_MACHINELOOPINFO_H
30#define LLVM_CODEGEN_MACHINELOOPINFO_H
31
32#include "llvm/Analysis/LoopInfo.h"
33#include "llvm/CodeGen/MachineBasicBlock.h"
34#include "llvm/CodeGen/MachineFunctionPass.h"
35#include "llvm/IR/DebugLoc.h"
36#include "llvm/Pass.h"
37
38namespace llvm {
39
Olivier Deprezf4ef2d02021-04-20 13:36:24 +020040class MachineDominatorTree;
Andrew Scull5e1ddfa2018-08-14 10:06:54 +010041// Implementation in LoopInfoImpl.h
42class MachineLoop;
43extern template class LoopBase<MachineBasicBlock, MachineLoop>;
44
45class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
46public:
47 /// Return the "top" block in the loop, which is the first block in the linear
48 /// layout, ignoring any parts of the loop not contiguous with the part that
49 /// contains the header.
50 MachineBasicBlock *getTopBlock();
51
52 /// Return the "bottom" block in the loop, which is the last block in the
53 /// linear layout, ignoring any parts of the loop not contiguous with the part
54 /// that contains the header.
55 MachineBasicBlock *getBottomBlock();
56
Andrew Scullcdfcccc2018-10-05 20:58:37 +010057 /// Find the block that contains the loop control variable and the
Andrew Scull5e1ddfa2018-08-14 10:06:54 +010058 /// loop test. This will return the latch block if it's one of the exiting
59 /// blocks. Otherwise, return the exiting block. Return 'null' when
60 /// multiple exiting blocks are present.
61 MachineBasicBlock *findLoopControlBlock();
62
63 /// Return the debug location of the start of this loop.
64 /// This looks for a BB terminating instruction with a known debug
65 /// location by looking at the preheader and header blocks. If it
66 /// cannot find a terminating instruction with location information,
67 /// it returns an unknown location.
68 DebugLoc getStartLoc() const;
69
Olivier Deprezf4ef2d02021-04-20 13:36:24 +020070 /// Returns true if the instruction is loop invariant.
71 /// I.e., all virtual register operands are defined outside of the loop,
72 /// physical registers aren't accessed explicitly, and there are no side
73 /// effects that aren't captured by the operands or other flags.
74 bool isLoopInvariant(MachineInstr &I) const;
75
Andrew Scull5e1ddfa2018-08-14 10:06:54 +010076 void dump() const;
77
78private:
79 friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
80
81 explicit MachineLoop(MachineBasicBlock *MBB)
82 : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
83
84 MachineLoop() = default;
85};
86
87// Implementation in LoopInfoImpl.h
88extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
89
90class MachineLoopInfo : public MachineFunctionPass {
91 friend class LoopBase<MachineBasicBlock, MachineLoop>;
92
93 LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
94
95public:
96 static char ID; // Pass identification, replacement for typeid
97
Olivier Deprezf4ef2d02021-04-20 13:36:24 +020098 MachineLoopInfo();
99 explicit MachineLoopInfo(MachineDominatorTree &MDT)
100 : MachineFunctionPass(ID) {
101 calculate(MDT);
Andrew Scull5e1ddfa2018-08-14 10:06:54 +0100102 }
103 MachineLoopInfo(const MachineLoopInfo &) = delete;
104 MachineLoopInfo &operator=(const MachineLoopInfo &) = delete;
105
106 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
107
Andrew Scullcdfcccc2018-10-05 20:58:37 +0100108 /// Find the block that either is the loop preheader, or could
Andrew Scull5e1ddfa2018-08-14 10:06:54 +0100109 /// speculatively be used as the preheader. This is e.g. useful to place
110 /// loop setup code. Code that cannot be speculated should not be placed
111 /// here. SpeculativePreheader is controlling whether it also tries to
112 /// find the speculative preheader if the regular preheader is not present.
113 MachineBasicBlock *findLoopPreheader(MachineLoop *L,
114 bool SpeculativePreheader = false) const;
115
116 /// The iterator interface to the top-level loops in the current function.
117 using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator;
118 inline iterator begin() const { return LI.begin(); }
119 inline iterator end() const { return LI.end(); }
120 bool empty() const { return LI.empty(); }
121
122 /// Return the innermost loop that BB lives in. If a basic block is in no loop
123 /// (for example the entry node), null is returned.
124 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
125 return LI.getLoopFor(BB);
126 }
127
128 /// Same as getLoopFor.
129 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
130 return LI.getLoopFor(BB);
131 }
132
133 /// Return the loop nesting level of the specified block.
134 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
135 return LI.getLoopDepth(BB);
136 }
137
138 /// True if the block is a loop header node.
139 inline bool isLoopHeader(const MachineBasicBlock *BB) const {
140 return LI.isLoopHeader(BB);
141 }
142
143 /// Calculate the natural loop information.
144 bool runOnMachineFunction(MachineFunction &F) override;
Olivier Deprezf4ef2d02021-04-20 13:36:24 +0200145 void calculate(MachineDominatorTree &MDT);
Andrew Scull5e1ddfa2018-08-14 10:06:54 +0100146
147 void releaseMemory() override { LI.releaseMemory(); }
148
149 void getAnalysisUsage(AnalysisUsage &AU) const override;
150
151 /// This removes the specified top-level loop from this loop info object. The
152 /// loop is not deleted, as it will presumably be inserted into another loop.
153 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
154
155 /// Change the top-level loop that contains BB to the specified loop. This
156 /// should be used by transformations that restructure the loop hierarchy
157 /// tree.
158 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
159 LI.changeLoopFor(BB, L);
160 }
161
162 /// Replace the specified loop in the top-level loops list with the indicated
163 /// loop.
164 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
165 LI.changeTopLevelLoop(OldLoop, NewLoop);
166 }
167
168 /// This adds the specified loop to the collection of top-level loops.
169 inline void addTopLevelLoop(MachineLoop *New) {
170 LI.addTopLevelLoop(New);
171 }
172
173 /// This method completely removes BB from all data structures, including all
174 /// of the Loop objects it is nested in and our mapping from
175 /// MachineBasicBlocks to loops.
176 void removeBlock(MachineBasicBlock *BB) {
177 LI.removeBlock(BB);
178 }
179};
180
181// Allow clients to walk the list of nested loops...
182template <> struct GraphTraits<const MachineLoop*> {
183 using NodeRef = const MachineLoop *;
184 using ChildIteratorType = MachineLoopInfo::iterator;
185
186 static NodeRef getEntryNode(const MachineLoop *L) { return L; }
187 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
188 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
189};
190
191template <> struct GraphTraits<MachineLoop*> {
192 using NodeRef = MachineLoop *;
193 using ChildIteratorType = MachineLoopInfo::iterator;
194
195 static NodeRef getEntryNode(MachineLoop *L) { return L; }
196 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
197 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
198};
199
200} // end namespace llvm
201
202#endif // LLVM_CODEGEN_MACHINELOOPINFO_H